As part of my exploration of different surface temperature datasets, I’m examining the relationship between average U.S. temperatures and other weather variables in NOAA’s Integrated Surface Hourly (ISH) dataset.
(I think I might have mistakenly called it “International” before, instead of “Integrated” Surface Hourly).
Anyway , one of the things that popped out of my analysis is related to our record warm March this year (2012). Connecting such an event to “global warming” would require either lazy thinking, jumping to conclusions, or evidence that the warmth was not caused by persistent southerly flow over an unusually large area for that time of year.
The U.S. is a pretty small place (about 2% of the Earth), and so a single high or low pressure area can cover most of the country. For example, if unusually persistent southerly flow sets up all month over most of the country, there will be unusual warmth. In that case we are talking about “weather”, not “climate change”.
Why do I say that? Because one of the basic concepts you learn in meteorology is “mass continuity”. If there is persistent and widespread southerly flow over the U.S., there must be (by mass continuity) the same amount of northerly flow elsewhere at the same latitude.
That means that our unusual warmth is matched by unusual coolness someplace else.